Piezo-resistive pressure sensors are known, and may include a silicon diaphragm with conductive or resistive areas on the surface of the diaphragm. The resistive areas are arranged so that, as the diaphragm deflects, some of the resistive areas increase in resistance, while other areas decrease in resistance or are relatively unchanged. Using appropriate output circuitry, such as a Wheatstone bridge, the output changes are generally proportional to the applied pressure and the resulting deflection of the diaphragm.
The resistance areas and immediately associated connections may be implemented by diffusion of n-type material or p-type material into the surface of the silicon diaphragm. One pair of resistors may have the resistive areas extending radially, while another pair of resistors may have the resistive areas extend circumferentially or perpendicular to a radial line from the center of the diaphragm. Coupling to external circuitry is normally accomplished by wire bonding to pad areas on the silicon diaphragm.
However, in some cases, failure or degradation of the operation of the pressure transducers as described above, have occurred.